Accompanying with the prolongation of human life span, the incidence of metabolic diseases such as osteoporosis, bone fracture, bone pain etc., recently increased. In bone tissue, bone formation and bone resorption are always occurring. While the balance of bone formation and bone resorption is kept in one's youth, bone resorption exceeds bone formation due to various causes as one's age increases (uncoupling). And when bone resorption prolongs for a long duration, bone tissue becomes fragile, which causes metabolic bone diseases such as osteoporosis, bone fracture, bone pain, etc. Therefore, if uncoupling can be inhibited, metabolic bone diseases such as osteoporosis, bone fracture, bone pain, etc. are expected to be prevented.
As conventional methods of preventing or treating metabolic bone diseases by inhibiting uncoupling, (1) calcium supplemented diets, (2) light exercise, (3) sunbathing, (4) medicinal therapy, etc. are exemplified. As for calcium supplemented diets, calcium salts such as calcium carbonate, calcium phosphate, etc., and naturally occurring calcium-containing preparation, such as bovine bone powder, egg shell, fish bone powder, etc. are used. They are, however, not necessarily good for oral intake. As light exercises, jogging or walking may be recommended. However, they are troublesome to a person who becomes weak and quite difficult to an immobilized aged person. Sunbathing is believed to be good for supplement of active form of vitamin D.sub.3 but is not sufficient. As medicinal therapy, 1.alpha.-hydroxyvitamin D.sub.3 and/or calcitonin may be used and they are known to be effective for treating osteoporosis. However, they are medicines themselves and cannot be used as food sources.
On the other hand, the present inventors found that the fraction obtained from whey protein was effective for strengthening bone (Japanese published unexamined patent application No. 183371 (1992)). Further, the present inventors found that the fraction obtained from the above bone strengthening fraction by treating with ethanol, heating, treating with salts or treating with ultrafiltration membrane was effective for stimulating osteoblastic proliferation (Japanese published unexamined patent application No. 176715 (1993) and for strengthening bone (Japanese published unexamined patent application No. 320066 (1993)). In addition, the present inventors found that basic protein fraction present in a very small amount of milk had actions of stimulating osteoblastic proliferation, strengthening bone and inhibiting bone resorption (Japanese patent application No. 207509 (1995)).
The present inventors, further, tried to separate, purify and identify active components of the basic protein having action of stimulating osteoblastic proliferation, strengthening bone and inhibiting bone resorption and eventually found that they were fragment 1.multidot.2 of kininogen which was already known. And the inventors also found that kininogen and degradation products of kininogen also had actions of promoting bone formation and inhibiting bone resorption and accomplished the present invention. Accordingly, an object of the present invention is to provide a novel agent promoting bone formation and inhibiting bone resorption comprising kininogen and/or degradation products of kininogen as an effective ingredient. Another object of the present invention is to provide a drink, food, medicine and feed promoting bone formation and inhibiting bone resorption combined with kininogen and/or degradation products of kininogen.